Conventional display screens, and in particular flat screens, are constituted by a rectangular light-emitting surface that is subdivided into vertical columns and horizontal rows. The columns and rows are made up of pixels, themselves being made up of sub-pixels of three different colors, generally red, green, and blue (“RGB screen”). Some screens make use of a number N of sub-pixels, and thus of colors, per pixel that is greater, e.g. four: red, green, blue, and yellow; or red, green, blue, and white.
The sub-pixels are generally in the form of small colored rectangles, or else they are more complex in structure, usually being inscribed in a rectangle, presenting a height that is about N times greater than their width so as to form pixels that are square, or more generally that are arranged in a grid having a square mesh.
The principle generally implemented consists in having columns of same-color sub-pixels extending over the full height of the screen, and in juxtaposing those columns horizontally. Thus, when considered along the vertical axis of a column, the short sides of the rectangles representing same-color sub-pixels are adjacent from one row to the next; they may be directly touching or they may be separated by a black line in order to increase the contrast of the image. Similarly, along the horizontal axis, the long sides of the rectangles are surrounded by rectangles of colors that are different, and they may also be spaced apart by black lines for increasing the contrast of the image.
Such a conventional structure is shown in FIG. 1, where reference P designates a pixel, SP designates a sub-pixel, C a column, L a row, ZN a black zone between two sub-pixels, and R, V, and B correspond to the sub-pixel colors: red, green, and blue.
FIG. 1 relates to the simplest configuration, in which the sub-pixels are rectangular. In commercially available screens there can be observed sub-pixels that present shapes that are complex (chevrons, double chevrons, combinations of squares and rectangles, etc.) with subdivisions that have been developed to improve the uniformity in brightness and contrast, observation angle, and more generally the apparent quality of the displayed image—i.e. the quality actually perceived by an observer. In particular with technologies that make use of liquid crystals, it is necessary to subdivide a sub-pixel into smaller entities, sometimes that are specifically addressable, each having different directional light efficiency. Even when the sub-pixels present a shape that cannot be inscribed in a rectangle (as in the Samsung LTI460HM03 screen, in which they have a double-chevron shape and in which they are interleaved), each sub-pixel of a row L is contiguous above and below with sub-pixels of the same color in rows L−1 and L+1.
That conventional structure leads to artifacts, particularly when the screen is observed from a short distance: black spaces between the rows can become visible, colored fringes can appear, etc. In addition, when such a screen is used with an angle selection array such as an array of cylindrical lenses for producing an autostereoscopic display, as explained in document EP 1 779 181, other artifacts are liable to appear, such as moiré patterns.